Gas Sensor

This application claims the benefit of priority to Japanese Patent Application No. 2024-080719 filed on May 17, 2024, the content of which is incorporated herein by reference in its entity.

The present invention relates to a gas sensor including a sensor element for detecting the concentration of a detection target gas.

As a gas sensor for detecting the concentration of oxygen or NOx in exhaust gas of an automobile or the like, a gas sensor having a plate-shaped sensor element is known. One of the gas sensors of this type is configured such that a periphery of a sensor element is retained by a tubular metal shell, an annular holder and an annular sleeve having element holes through which the sensor element is inserted are provided in an internal hole of the metal shell, and filling powder such as a talc ring is provided between the holder and the sleeve to fill a gap between the metal shell and the sensor element (Japanese Patent Application Laid-Open (kokai) No. 2019-138679).

Here, the sleeve is crimped so as to be pressed toward the holder, whereby the filling powder is compressed to enter a gap between the metal shell and the sensor element, thus performing a sealing function.

Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2019-138679

However, in a conventional gas sensor, as shown in, the peripheries of a holderand a sleevearound an element holehave flat surfaces. Therefore, when filling powderis compressed via the sleeve, a pressure concentrates on cornersof a sensor element, which have low strength, so that the sensor elementmight be damaged.

The reason is as follows. That is, for example, if the periphery of the holderaround the element holehas a flat surface, when the filling powderis compressed, the sensor elementat the periphery of the element holeis uniformly subjected to pressing forces F from the filling powder. However, this causes the low-strength cornersto be subjected to the pressing forces F along with the other parts, leading to damage of the corners

Meanwhile, since the filling powderfills (seals) the gap between the metal shell and the sensor element, it is difficult to weaken the entire pressing forces F.

Accordingly, an object of the present invention is to provide a gas sensor configured to suppress damage when a sensor element is attached.

In order to solve the above problem, a gas sensor of the present invention is a gas sensor comprising: a plate-shaped sensor element extending in an axial-line direction and having a detection portion on a front end side thereof, said detection portion configured to detect target gas; a tubular metal shell surrounding and retaining a periphery of the sensor element in a radial direction; a tubular holder retained in an internal hole of the metal shell and having a first element hole which has a rectangular shape and through which the sensor element is inserted; a tubular sleeve retained in the internal hole of the metal shell on a rear end side relative to the holder, and having a second element hole which has a rectangular shape and through which the sensor element is inserted; and filling powder provided in the internal hole of the metal shell, between the holder and the sleeve, so as to fill a gap between the metal shell and the sensor element. At least one of the holder and the sleeve has a flat surface contacting the filling powder, and a protrusion protruding from the flat surface toward the filling powder and surrounding the first element hole or the second element hole. The protrusion is tapered toward the filling powder, as seen from a direction perpendicular to a main surface of the sensor element, and a boundary portion, in which corners of the sensor element extending in the axial-line direction thereof abut on the protrusion, is located between a top portion of the protrusion and a base portion where the protrusion connects to the flat surface.

In this gas sensor, when the filling powder is compressed, a pressing force from the filling powder applied to the sensor element near the boundary portion becomes a highest pressing force on a side near the top portion, and becomes a pressing force lower, at the boundary portion. Then, the pressing force is further reduced from the boundary portion toward the base portion, and becomes a lowest pressing force at the base portion and the flat surface.

Thus, the pressing force from the filling powder weakens along the axial-line direction of the corners. Therefore, the corners having a low strength are prevented from being subjected to a high pressing force that is applied to the other parts (e.g., a part where the sensor element abuts on the top portion), whereby damage when the sensor element is attached can be suppressed.

Meanwhile, in the vicinity of the top portion, the distance to the sleeve is short and the pressing force is high, so that the gap between the metal shell and the sensor element can be assuredly filled (sealed) with the filling powder.

In the gas sensor of the present invention, as seen from the direction perpendicular to the main surface of the sensor element, a relationship of c<a<b is satisfied, where a is a width of the sensor element, b is a width of the base portion where the protrusion connects to the flat surface and c is a width of the top portion of the protrusion.

In this gas sensor, it is possible to assuredly locate the boundary portion between the top portion and the base portion.

In the gas sensor of the present invention, the top portion of the protrusion may be flat.

In this gas sensor, the filling powder in a region around the sensor element can be compressed at surfaces, as compared to a case where the top portion has a steep mountain shape. Thus, the periphery of the sensor element can be stably filled with the filling powder, and the gap between the metal shell and the sensor element can be more assuredly filled (sealed).

In the gas sensor of the present invention, the protrusion may reach an end of the flat surface.

In this gas sensor, when the protrusion reaches the end of the flat surface, accordingly, the area where the filling powder in a region around the sensor element can be compressed with a high pressing force increases. Thus, the gap between the metal shell and the sensor element can be more assuredly filled (sealed).

In the gas sensor of the present invention, the gas sensor may be an oxygen sensor or a NOx sensor.

The present invention makes it possible to provide a gas sensor configured to suppress damage when a sensor element is attached.

Hereinafter, an embodiment of the present invention will be described.

is an entire sectional view along a longitudinal direction of a gas sensor (oxygen sensor)according to an embodiment of the present invention.is a perspective view of a sensor element.is a perspective view of a holder.is a perspective view of a sleeve.

The gas sensoris an oxygen sensor for detecting the concentration of oxygen in exhaust gas of an automobile or various internal combustion engines.

In, the gas sensorincludes: a tubular metal shellhaving, on an outer surface, a thread portionto be fixed to an exhaust pipe; the sensor elementhaving a plate shape and extending in an axial-line-O direction (the longitudinal direction of the gas sensor, i.e., the up-down direction in the drawing); the tubular sleevemade of ceramic and provided so as to surround the radial-direction periphery of the sensor element; the tubular holdermade of ceramic (alumina); a tubular separatormade of ceramic and provided in a state of surrounding the periphery of the rear end of the sensor elementinside the front end side of an insertion holepenetrating in the axial-line direction; and four metal terminals(only two of them are shown in) provided between the sensor elementand the separator.

A detection portionat a front end of the sensor elementis covered with a porous protection layerof alumina or the like (see).

The metal shellis made of stainless steel, has a through holepenetrating in the axial-line direction, and is formed substantially in a tubular shape having a ledge portionprotruding radially inward of the through hole. In the through hole, the sensor elementis placed such that a front end portion of the sensor elementprotrudes frontward relative to the front end of the through hole. The ledge portionis formed as an inward taper surface sloped relative to a plane perpendicular to the axial-line direction.

Inside the through holeof the metal shell, the holder, a filling powder(hereinafter, may be referred to as talc ring), and the aforementioned sleeveare stacked in this order from the front side to the rear side so as to surround the radial-direction periphery of the sensor element.

A crimp packingis provided between the sleeveand a rear end portionof the metal shell. The rear end portionof the metal shellis crimped so as to press the sleevetoward the front side via the crimp packing.

On the other hand, as shown in, around the outer periphery at the front side (downward side in) of the metal shell, a single-wall protectorhaving a plurality of holes and made of metal (e.g., stainless steel) is attached by welding or the like so as to cover a protruding part of the sensor element.

An outer casingis fixed to the outer periphery at the rear side of the metal shell. At an opening on the rear side (upward side in) of the outer casing, a grommetmade of rubber is provided, and four lead wires(only two of them are shown in) electrically connected to the four metal terminals(only two of them are shown in) of the sensor elementpass through lead wire passage holes (not shown) formed in the grommet.

The grommetis retained inside the outer casingwith the grommetcrimped from the outer side of the outer casing.

The separatoris provided at the rear end side (upward side in) of the sensor elementprotruding from the rear end portionof the metal shell. The separatoris provided around a total of four electrode pads(only two electrode pads are shown in) formed on main surfaces at the rear end side of the sensor element. The separatoris formed in a tubular shape having the insertion holepenetrating in the axial-line direction, and has a flange portionprotruding radially outward from the outer surface. The separatoris held inside the outer casingby the flange portioncontacting with the outer casingvia a holding member.

As shown in, the sensor elementhas a plate shape extending in the axial-line-O direction, and a front end portionthereof serves as the detection portionfor detecting the concentration of oxygen. The detection portionis covered with the porous protection layer. The sensor elementitself has a known configuration, i.e., although not shown, has the detection portion having an oxygen-ion-permeable solid electrolyte and a pair of electrodes, and a heater portion for heating the detection portion to keep the temperature thereof constant.

Four cornersare formed in parallel to the axial-line-O direction of the sensor element.

At a rear end side on one main surfaceof the sensor element, two electrode padsare arranged in the direction of a width W, and a sensor output signal from the detection portionis output from the electrode padsvia a lead portion (not shown). In addition, at the rear end side on another main surfaceopposite to the main surface, two electrode padsare arranged in the direction of the width W, whereby power is supplied to the heater portion via a lead portion (not shown).

Each electrode padhas a rectangular shape elongated in the axial-line-O direction, and can be formed as a sintered body containing Pt as a main component, for example.

is a perspective view of the holder.

The holderhas a tubular shape, and has a first element holewhich has a rectangular shape and through which the sensor elementis inserted.

The holderhas a flat surfacecontacting the filling powder(on the upper side in), and a protrusionprotruding from the flat surfacetoward the filling powder(on the upper side in) and surrounding the first element hole

The protrusionhas substantially a trapezoidal shape tapered toward the filling powder(on the upper side in), as seen from a direction D perpendicular to the main surfaceof the sensor element.

The flat surfaceis formed on the radially outer side of the first element hole, and the protrusionis formed so as to surround the first element holefrom the flat surfacetoward the radially inner side.

The protrusionhas a top portion, and a base portionat which the protrusionconnects to the flat surface

In this example, a slope surfacehaving a slope shape is formed between the top portionand the base portion. The shape of the protrusionbetween the top portionand the base portionis not limited and may be a stepped shape, for example.

In this example, the top portionis flat (surface).

A peripheral edgem at which the first element holeintersects the protrusionhas a contour that extends in parallel to the main surface, at the top portion, then extends toward the front end side in the axial-line-O direction along the slope surface, and extends in the direction D from a certain position on the slope surface

Thus, a boundary portion BR (BR also corresponds to the peripheral edge) where the four corners(three of them are shown in) of the sensor elementabut on the protrusionin a state in which the sensor elementis inserted through the first element hole, is located at a certain position on the slope surface, i.e., between the top portionand the base portion. The reason will be described later.

is a perspective view of the sleeve. The sleevehas the same configuration as the holder, and therefore the overview thereof will be described.

Specifically, the sleevehas a tubular shape, and has a second element holewhich has a rectangular shape and through which the sensor elementis inserted.

The sleevehas a flat surfacecontacting with the filling powder(on the upper side in), and a protrusionprotruding from the flat surfacetoward the filling powder(on the upper side in) and surrounding the second element hole